Homemade device for measuring hydrogen production

I am an inventor, who has been working on an alloy for electrolysis, which permits low energy input for reaction (1.5V at 300mA), sustains a vigorous reaction and is non-sacrificial in the reaction. After three years of research and development on a shoestring, I finally have a modified Hoffman Apparatus, which is very productive. I want to measure the hydrogen output of the device (liters per hour) and have been stumped on my several attempts to measure the volume.

I made a multi-plate anode/cathode device from PVC and it appears to contain the hydrogen well without too many leaks. I tried to make a device, which operated on water evacuation (gas displacing water in a measured container) and it worked well for the first three minutes capturing about 1/3 liter of hydrogen. Thereafter, it seemed as though the electrolysis device had stopped producing (not the case, it was actually building up a lot of pressure between the electrolyser and the container without apparently displacing any more water).

Someone told me that I should use an inverted container within a larger water container with a small diameter tube running through the top of the submerged container - forming a "J" and that would capture low-pressure hydrogen gas production.

Any comments or assistance, by way of pointing my nose in the direction of drawings for homemade measurement device would be greatly appreciated.

If you want to know where I'm heading with this research Email me and I'll give you the URL for my R&D project.